In the age of science and technology, computers have been indispensables for people and closely involved in the living of people. Every profession needs computers to aid operation. No matter desktops or notebooks, computers are widely used in various occasions. However, a user is usually hard to operate a keyboard in a dim or dark environment. Therefore, manufacturers had developed various self-luminous keyboards to enable users to accurately press correct keys, such as those disclosed by U.S. Pat. No. 6,179,432, U.S. Pat. No. 6,199,996, U.S. Pat. No. 6,284,988, U.S. Pat. No. 6,322,229, and U.S. Pat. No. 6,554,442, and Taiwan patents No. 438035, No. 465777, No. 468833, No. 509955, No. 516671, No. 535385, No. 570235, and No. 1242737. In the abovementioned prior-art patents, a light emitting plate is installed inside a keyboard to illuminate the keycaps and enable user to operate the keyboard in a dim or dark environment.
However, the entire keyboard is entirely and uniformly backlighted by the light emitting plate in the abovementioned prior-art patents, wherein the elastic members and the actuation mechanisms are arranged between the light emitting plate and the keycaps, and the elastic members, the actuation mechanisms and keycaps are usually made of a light-permeable material. In some prior-art patents, the keycaps are made of an opaque material, and the characters and symbols on the keycaps are made of a light-permeable material. The self-luminous keyboard is usually operated in a dim or dark environment, such as in an airliner or a vehicle. Thus, the intense light of the entirely and uniformly luminous keyboard may influence others and makes the user hard to recognize the individual characters or symbols on the keycaps. Even though the characters and symbols are made of a transparent material and the keycaps are made of an opaque material, the light projected from the gaps between the adjacent keycaps still makes the user hard to recognize the characters. For the case that the characters and symbols are made of an opaque material and the keycaps are made of a transparent material, the result is the same. For a user who is unfamiliar with the keyboard and cannot precisely memorize the positions of the characters, the situation is particularly serious, and he may thus input wrong instructions.